Zhang Xu (张旭,fl. 8th century), courtesy name: Bogao (伯高), was a Chinese calligrapher of the Tang Dynasty.
A native of Suzhou, he became an official during the reign of Emperor Xuanzong of Tang. Zhang was known as one of the Eight Immortals of the Wine Cup. Legend has it that whenever he was drunk, he would use his hair as brush to perform his art, and upon his waking up, he would be amazed by the quality of those works but failed to produce them again in his sober state.
Though more well-known for his explosive cursive script, he excelled in the regular script. Anecdotes go that he grasped the essence of cursive writing by observing some porters fight for their way with the guard of honor of some princess, and by watching the solo performance of a famous sword-dancer.
He is often paired with the younger Huai Su (怀素) as the two greatest cursive calligraphers of the Tang Dynasty. The duo is affectionately referred to as "the crazy Zhang and the drunk Su" (颠张醉素).
Zhang Xu's running script calligraphy shows much diversity. According to a modern scholar, Han Yutao, Zhang's calligraphy works have three properties. First, they were wild. He always finished a calligraphic work in one sweep.
Hence, when reading his calligraphy work, one can feel the momentum. Second, they were strange and always varied. Zhang's calligraphy is as unpredictable as his brushstrokes and character structures are unfathomable. Third, they were formidable. Previous Chinese calligraphic works had a slender beauty, while the calligraphy work of Zhang Xu makes the reader feel as if one's head were pressed down by stones. Reading Zhang's calligraphy, one may have the feeling of being threatened by a sword. Yet, he respects his dignity. Though Zhang Xu's kuangcao were wild and crazy, his brushstroke technique adhered to certain rules, and he was also proficient at the more restrained kaishu calligraphy. Only a few of Zhang Xu's works have remained to this day, and among the masterpieces are Gushi Sitie and Shiwuri Tie.